Power packs are often used to power mobile devices, such as cellular telephones, personal digital assistants (PDAs), media players and the like. Typically, power packs include rechargeable electrochemical cells or batteries, which are charged using a dedicated charger unit drawing power from some power source such as the mains or a vehicle battery and which may be external or internal to the device.
Charger units powered from mains or power lines usually consist of a bulky plug box, containing a step-down transformer and a rectifier, with conducting pins for connecting to the mains socket. When in use, the plug box is plugged into a mains socket and a trailing cord connects to the device via a connecting plug. If the trailing wire is snagged or jerked the wire and connectors may be damaged or the device may be pulled to the ground. Moreover, the trailing wire itself is inconvenient and unsightly particularly where a number of devices are charged from a common power socket and the trailing wires may become entangled.
Systems are known involving various add-on inductive power receivers which are retrofittable to portable electrical devices. Such receivers which may be retrofitted to the power packs of electrical devices. Note that, in such systems, the inductive unit is an external unit which connects to the power pack via its conductive contacts.
A prior art system is described in PCT/KR2007/004418 to Jung, titled “Non-contact charger system of wireless power transmission for battery and control method thereof”. Jung's patent application describes a wireless charger system for a battery pack which may include a receiving unit incorporated into the housing of the battery pack. In Jung's receiver a number of separate electronic blocks are described including a secondary core block, a secondary rectification block, a battery charging block, a charge monitoring block and a battery protection block each of which controls a different aspect of the charging process. Because all the separate circuit blocks are incorporated into the battery pack housing, they must share available space with the electrochemical cells. Consequently, the size of the battery and its capacity may be compromised in order to provide space for the control circuitry for inductive charging.
There is, therefore, a need for an inductive receiving unit for integration into the housing of a battery pack with minimal circuit blocks and overall smaller dimensions. Embodiments described herein address this need.